Coal constituents for coking



Patented Aug. 4, 1936 a UNITED mm COAL CONSTITUENTS FQR COKING Frank F; Marquard, Clairton, Pa.

No'Drawing. Original application February 3, 1932, Serial No. 590,781. Divided and this ap-- plication June 17, 1935, Serial No. 27,128

1 Claim.

I This invention relates to the manufacture of coke, and more particularly to the coal constituents for coking and has among its objects the provision of a novel method to condition the coals and provide for a better grade of product than has heretofore been'possible.

The method of this invention is particularly adapted to low grade bituminous coals, and partially consists in reducing the amount of bone and slate between the sizes of 7 and 20 mesh in the crushed coal to a point less than .3 per cent to sink at specific gravity of 1.55, whereby the coal is conditioned to such degree that the coke produced thereby will have a hardness and toughness range equal to good metallurgical coke for use in blast furnaces. This method-of treating coal is disclosed and claimed in an application entitled Treating bituminous coal for coking, filed February 3, 1932 and bearing Serial N 0. 590,781, the present case being a division therefrom.

As pointed out in the co-pending application referred to, it has long been observed that coking coals, when subjected to heat, produce coke of varying degrees of hardness and toughness and,

since the coke produced must stand a definite test of toughness and hardness to enable its handling and use without excessive breakage, it became the object of the coke manufacturer to make a careful study of the coking temperatures, crushing, mixing, wetting and various other phases of processing and conditioning of coal to secure the proper results of hardness and toughness in the resultant coke so essential for most uses; such as metallurgy, blast furnace operation, etc.

Various degrees of crushing of high volatile coals and mixing with low volatile coals have provided an improved coke structure but only at considerable extra expense; due to the cost of the operations and the added cost for freight on distantly located coals.

To eliminate this added expense has been the constant problem of the metallurgical coking engineers.

Aside from the coking properties of bituminous coals it is recognized that many of these coals were very high in ash and sulphur, and it is ad-' visable, therefore, to clean these coals to free them from slate and bone coal in order-to render the coke from these coals sufiiciently low in ash and sulphur to make them desirable chemically for metallurgical use, particularly in blast furnaces.

Such treating orcleaning of the coals improved the chemistry of the coke and, in most cases, considerably improved the physical properties of the coke also. However, there exists large quantities of bituminous coals which do not possess suflicient coking properties, even after they have been washed in the usual best approved methods of 5 cleaning.

The invention of my co-pending application, Serial No. 590,781, provides a method whereby this heretofore useless coking coal may be used to procure a commercial metallurgical coke. l0 I-Ieretofore, in all washing or cleaning operations the object has been to remove the slate and bone and sulphur to a point within practical limits without losing too much coal in the process of cleaning and, since the larger pieces of slate and 15 pyrite could be removed quite readily in normal washing operations, these larger pieces were removed and the smaller pieces of slate and bone, which were more difiicult to remove, were permitted to remain in the clean coal. The im- 20 portance of the removal of such small pieces, aside from the reduction in ash, was not known to the art, since a large bulk of the slate and bone (by weight) was in the larger pieces.

By the removal of the larger pieces which 25 formed the large bulk of the slate and bone (by weight) it was apparent to those skilled in the art that the removal of the smaller particles of slate would have a very limited influence upon the further reduction of the ash analysis of the 30 clean coal. Therefore, these small pieces of bone or slate were only removed to a point practical from an ash standpoint of cleanliness.

I have now discovered that the small pieces of slate remaining in the washed coal, although (by 35 weight) they amount to less than 10 per cent of the total slate in the coal before washing, are detrimental to the physical structure of the coke about in the proportion to their numbers and not to their weight, because each piece of slate 40 above the size that will pass a 20 mesh sieve will set up a microscopic hair line fracture in the resulting coke.

By tests that have been made I have found that one piece of slate weighing a pound, when 45 broken down to pass a screen and remaining on a 20 mesh screen will contain approximately 52,900 pieces and will produce, therefore, 52,000 hair line fractures in the coke. This weakens the coke structure and renders it unfit for use in a 50 metallurgical blast furnace.

I clean the low grade bituminous coals with special care to remove the small pieces of slate and bone so as to reduce the amount of slate and bone between the sizes of and 20 mesh in 55 the clean coal to a point less than .3 per cent to sink at specific gravity of 1.55 in accordance with my co-pending application, previously described.

By this method of cleaning coals I have greatly extended the use of low grade coking coals which otherwise could not be utilized for some purposes, such as making metallurgical coke. Thus, I have increased the available supply 'of coking coals for, by way of example, the manufacture of good metallurgical coke.

During the cleaning operation special provisions are made for removing a much larger percentage of the small sizes of bone and slate, sizes ranging from to 20 mesh, than is removed in the normal process of coal washing.

These small sizes of bone and slate may contain considerable coal and are generally known as middlings. I have found that if these middlings are crushed to a size under 20 mesh they will not have a detrimental effect upon the physical structure of the coke, as they have when not crushed. The pulverized middlings are then added to'the cleaned coal, and the aggregate used as the coal constituents to be used for coking.

When not crushed these small pieces of slate tend to form hairline fractures in the coke and thus cause the coke made from the coal constituents to break more easily. Therefore, the important part of the washing operation when improvement in the physical structure of the coke is of paramount importance is to carry on in such a manner that a maximum amount of the small size slate to 20 mesh is eliminated from the constituents While I have described certain specific steps of my invention, it will be understood that I do not wish to be limited exactly thereto, since various modifications may be made without departing from the scope thereof, as defined by the following claim.

I claim:

The method of preparing coal constituents for coking which consists in the removal from low grade bituminous coal of the small size bone and slate to 20 mesh or under to a point so that the resulting coal of the size to 20 mesh will 20 contain not over approximately .3 per cent to sink at 1.55 gravity and then crushing the removed constituents to a size under 20 mesh screen and adding this crushed product to the cleaned coal for coking.

FRANK F. MARQUARD. 

